Foams of a variety of plastic materials, densities and other physical characteristics have long been used for a wide variety of purposes, including structural fillers, thermal insulation, and as forms or cushions in packaging. In the packaging field, rigid polystyrene foam may be pre-cast or otherwise formed to receive and cradle for protection products which might otherwise be damaged in transporting them from place to place. In modern packaging, the supporting foam is formed in situ between the articles to be protected and an outer container such as a corrugated box. Plastic foams used in this way take the place of such packing materials as excelsior, corrugated paper products and a variety of formless packing materials. In general, the use of plastic foams reduce labor and material costs and save weight to thereby save transportation costs.
The instant invention is particularly concerned with the provision of plastic foam bodies formed in situ from liquid component materials which, when mixed together, generate a foam which after a short interval becomes a stable, semi-rigid and somewhat flexible foam body. Depending upon the nature of the chemical materials, one of the liquid components may be essentially a catalyst as in the formation of polyurethane foam.
In this packaging system as presently employed, the liquid components are supplied under pressure to a control gun which is equipped with valves which control the flow of the liquids to a mixing chamber to which air or other inert gas is also directed so that the components are mixed to initiate the foaming action. The mixture is then propelled through the gun's nozzle by the compressed air and directed to the container. When the amount supplied is sufficient to fill the container when the foaming action is complete, the flow of the liquid components is stopped by manipulating the valves in the gun, usually by means of a trigger. The process may then be repeated to fill another container. Usually provision is made to blow out as much as possible of the mixture to minimize the amount left inside of the gun to set and require removal by mechanical and/or solvent means. Special cleaning procedures are usually required when the gun is to be laid aside for a long period of time.
Many attempts have been made to minimize the problem of keeping these guns clean of reacted plastic material to avoid interference with its proper operation. In general, the problem has been attacked by minimizing the size of the reaction chamber and making it more accessible for cleaning.
The object of the present invention is to provide a new method and novel gun for effecting the mixing of liquid components in the in situ formation of foam. More specifically, the invention provides means for bringing the liquid components together at a point in space forwardly of the gun, preferably but not necessarily along with a continuous supply of air or other inert gas at which point foaming reaction is initiated and the plastic foaming mixture is propelled in the direction in which the gun is aimed to place the foam in the desired locations, e.g., within a container. Because the liquid components are not brought together in any way within the body of the gun, the problem of keeping the gun passages free of reacted plastic material is entirely obviated.
Another object is to provide a flexible extension of the liquid component and air channels forwardly from the nozzle of the gun to permit direction of the foam stream more accurately into otherwise hard-to-reach places.
A further object is to provide means for air-purging the liquid component channels to even further minimize maintenance cleaning of the gun after use.
Further objects and the achievements of this invention will appear as the description thereof proceeds.